This invention relates to the field of medical devices, and more particularly to a catheter balloon having a taper with a non-circular transverse cross section.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter, and the stent is left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. Angioplasty balloons preferably have high strength for inflation at relatively high pressure, and high flexibility and softness for improved ability to track the tortuous anatomy and cross lesions. The balloon compliance is chosen so that the balloon will have a desired amount of expansion during inflation. Compliant balloons, for example balloons made from materials such as polyethylene, exhibit substantial stretching upon the application of tensile force. Noncompliant balloons, for example balloons made from materials such as PET, exhibit relatively little stretching during inflation, and therefore provide controlled radial growth in response to an increase in inflation pressure within the working pressure range.
In order to decrease the cross sectional profile of the balloon catheter to thereby facilitate advancement of the catheter within the patient""s vasculature and across a stenosed region, balloons may be folded into a low profile configuration having balloon wings wrapped around the balloon prior to insertion into the patient. However, one difficulty has been after the balloon is inflated in the patient, the balloon tends to deflate to form a large flat wing or a bunched irregular shape. The resulting relatively large profile of the deflated balloon tends to complicate repositioning or removal of the balloon in the vasculature.
It would be a significant advance to provide a catheter balloon with improved refold upon deflation after inflation of the balloon.
The invention is directed to a balloon catheter including an elongated shaft and a balloon on a distal shaft section having a working section, and tapered sections having an inflated configuration with a non-circular transverse cross section (hereafter xe2x80x9cnon-circular tapersxe2x80x9d). In one embodiment, the noncircular tapers are triangular, although alternative non-circular cross sectional designs may be used, such as lobed tapers. The non-circular tapers deflate to form two or more deflated wings along at least a section of the deflated balloon. The deflated wings provide a deflated balloon with a relatively low profile, which facilitates repositioning or removal of the balloon catheter within the patient""s vasculature.
The balloon catheter of the invention generally comprises an elongated shaft having proximal and distal ends and at least an inflation lumen, and a balloon on a distal shaft section having an interior in fluid communication with the inflation lumen. The balloon has a working section which in a presently preferred embodiment has a cylindrical inflated configuration. The balloon working section or length is typically centrally located and is configured to inflate to perform a therapeutic or diagnostic medical procedure such as dilatation of a stenosis, deployment of a stent, or delivery of a medium. A proximal non-circular tapered section is proximal to the working section, and a distal non-circular tapered section is distal to the working section
The non-circular tapered section of the balloon has a plurality of side sections and cusps between adjacent side sections. The balloon deflates with a fold along the line of the each cusp, to thereby form a plurality of deflated wings. In a presently preferred embodiment, the tapered section has three cusps to thereby form three deflated wings. However, in alternative embodiments, the tapered section may have two cusps or more than three cusps, depending on the non-circular shape of the tapered section. A tapered section with three cusps, such as in a triangular cross section, is generally preferred over shapes with four or more cusps due to the lower volume and the smaller outer diameter provided by the tri-cusped tapered section.
The non-circular configuration of the tapers provides tapered sections having a reduced volume compared with conventional conical tapered sections. Preferably, the non-circular tapered section has an inflated inner volume which is not greater than about 75% of the inflated inner volume of a conventional conical tapered section. As a result, the balloon of the invention inflates and deflates faster than a balloon having a conical tapered section due to the reduced inner volume of the balloon of. the invention, and without reducing. the inflated outer diameter of the working section.
In one embodiment, the balloon includes a proximal conical tapered section between the working length and at least a portion of the proximal non-circular tapered section, and a distal conical tapered section between. the working length and at least a portion of the distal non-circular tapered section. The conical section preferably slopes away from the working length at a steeper angle than conventional conical tapered sections. The non-circular tapered sections preferably taper at the same angle than conventional conical tapered sections. However, the non-circular tapered sections may taper at a smaller angle than conventional tapers, i.e., a more gradual taper, which, due to the reduced volume of the non-circular configuration, will not: impact the inflation/deflation time of the balloon. The balloon of the invention is configured to minimize contact between the patient""s vessel wall and the sections of the balloon beyond either end of the working length.
In one embodiment in which the balloon is preferably formed of a material such as nylon and has noncompliant to semicompliant expansion, the non-circular tapered sections inflate to form non-circular transverse cross sections at any pressure from above atmospheric pressure to the burst pressure of the balloon. In another embodiment in which the balloon is preferably formed of a relatively soft material such as polyether block amides and polyurethanes and has semicompliant to complaint expansion, the non-circular tapered sections inflate to form non-circular transverse cross sections at any pressure within the working pressure range of the balloon. In one embodiment, the tapered sections inflate to the non-circular shape at an inflation pressure of at least about 15 psi (atmospheric pressure) to about 60 psi, and most preferably about 15 psi to about 30 psi. Depending on the material used to form that balloon, the balloon will rupture with the non-circular tapered sections retaining the non-circular shape. In one embodiment, inflated tapered sections retain the non-circular shape over a pressure range of about 15 psi to about 300 psi, and more specifically about 15 psi to about 265 psi.
One embodiment comprises a method of performing a medical procedure generally including positioning within a body lumen a balloon catheter comprising an elongated shaft having a proximal end, a distal end, and an inflation lumen, and a balloon on a distal shaft section having an interior in fluid communication with the inflation lumen, the balloon having a working section having a cylindrical inflated configuration, and a proximal tapered section proximal to the working section and a distal tapered section distal to the working section, the tapered sections having an inflated configuration with a non-circular transverse cross section. The balloon is inflated within the body lumen from an uninflated configuration to the inflated configuration, the inflated non-circular tapered sections having a smaller inflated diameter than the inner diameter of the body lumen so that the non-circular tapered sections do not inflate against a wall defining the body lumen. The balloon is inflated, with the working length in the cylindrical inflated configuration to perform a procedure such as dilatating a lesion or implanting a stent in the patient""s blood vessel. The balloon is deflated to a deflated configuration in which the balloon collapses along a line of the cusps of the non-circular tapered sections to form at least two deflated wings in at least a section of the balloon, and preferably in the working section of the deflated balloon. The catheter is repositioned within or removed from the body lumen with the balloon in the deflated configuration.
The balloon of the invention has improved inflation/deflation times due to the lower volume of the. non-circular tapered section compared with a conventional conical tapered section. Additionally, the non-circular tapered section has a smaller inflated profile, which eliminates or reduces contact between the patient""s vessel wall and the sections of the balloon proximal and distal to the balloon working length and the resulting damage to the patient""s blood vessel caused by inflation of the tapered sections against the blood vessel wall. Moreover, the balloon of the invention has a low profile deflated configuration due to the non-circular tapered section which deflates to form two or more deflated wings along a length of the deflated balloon. These and. other advantages of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings.